Lithographic apparatus and device manufacturing method

ABSTRACT

An immersion lithographic projection apparatus is disclosed in which a liquid removal system surrounds a liquid supply system which provides liquid to a space between a projection system and a substrate. The liquid removal system is moveable relative to the liquid supply system and is controlled to have substantially zero velocity relative to the moving substrate table. The gap between the liquid supply system and the liquid removal system may be covered and the atmosphere between the liquid supply system and the liquid removal system above the substrate table may be maintained such that the vapor pressure of liquid is relatively high.

FIELD

The present invention relates to a lithographic apparatus and a methodfor manufacturing a device.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. The point of this is to enableimaging of smaller features since the exposure radiation will have ashorter wavelength in the liquid. (The effect of the liquid may also beregarded as increasing the effective NA of the system and alsoincreasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein.

However, submersing the substrate or substrate and substrate table in abath of liquid (see, for example, U.S. Pat. No. 4,509,852) means thatthere is a large body of liquid that must be accelerated during ascanning exposure. This requires additional or more powerful motors andturbulence in the liquid may lead to undesirable and unpredictableeffects.

One of the solutions proposed is for a liquid supply system to provideliquid on only a localized area of the substrate and in between thefinal element of the projection system and the substrate using a liquidconfinement system (the substrate generally has a larger surface areathan the final element of the projection system). One way which has beenproposed to arrange for this is disclosed in PCT patent applicationpublication no. WO 99/49504. As illustrated in FIGS. 2 and 3, liquid issupplied by at least one inlet IN onto the substrate, preferably alongthe direction of movement of the substrate relative to the finalelement, and is removed by at least one outlet OUT after having passedunder the projection system. That is, as the substrate is scannedbeneath the element in a −X direction, liquid is supplied at the +X sideof the element and taken up at the −X side. FIG. 2 shows the arrangementschematically in which liquid is supplied via inlet IN and is taken upon the other side of the element by outlet OUT which is connected to alow pressure source. In the illustration of FIG. 2 the liquid issupplied along the direction of movement of the substrate relative tothe final element, though this does not need to be the case. Variousorientations and numbers of in- and out-lets positioned around the finalelement are possible, one example is illustrated in FIG. 3 in which foursets of an inlet with an outlet on either side are provided in a regularpattern around the final element.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4. Liquid is supplied by two groove inlets IN oneither side of the projection system PL and is removed by a plurality ofdiscrete outlets OUT arranged radially outwardly of the inlets IN. Theinlets IN and OUT can be arranged in a plate with a hole in its centerand through which the projection beam is projected. Liquid is suppliedby one groove inlet IN on one side of the projection system PL andremoved by a plurality of discrete outlets OUT on the other side of theprojection system PL, causing a flow of a thin film of liquid betweenthe projection system PL and the substrate W. The choice of whichcombination of inlet IN and outlets OUT to use can depend on thedirection of movement of the substrate W (the other combination of inletIN and outlets OUT being inactive).

In European patent application publication no. EP 1420300 and UnitedStates patent application publication no. US 2004-0136494, each herebyincorporated in their entirety by reference, the idea of a twin or dualstage immersion lithography apparatus is disclosed. Such an apparatus isprovided with two tables for supporting a substrate. Levelingmeasurements are carried out with a table at a first position, withoutimmersion liquid, and exposure is carried out with a table at a secondposition, where immersion liquid is present. Alternatively, theapparatus has only one table.

Handling liquid in an immersion lithographic projection apparatus maypresents various challenges including containment of the liquid,temperature control and/or interaction of the liquid with the top coaton the substrate.

SUMMARY

It is desirable, for example, to provide an apparatus in which one ormore possible disadvantages of the presence of immersion liquid arealleviated.

According to an aspect of the invention, there is provided alithographic projection apparatus, comprising: a projection systemconfigured to project a patterned beam of radiation onto a substrate; aliquid supply system configured to provide a space between theprojection system and a substrate with a liquid; and a liquid removalsystem comprising a barrier configured to at least partly contain liquidwhich has escaped from the liquid supply system surrounding the liquidsupply system, the barrier being moveable relative to the liquid supplysystem and having a seal mechanism configured to seal between thebarrier and the substrate, a substrate table configured to hold thesubstrate, or both.

According to an aspect of the invention, there is provided alithographic projection apparatus, comprising: a substrate tableconfigured to hold a substrate; a projection system configured toproject a patterned beam of radiation onto the substrate; and a sealdevice configured to surround a substrate and to at least partly containa liquid on a surface of the substrate, the substrate table, or both,the seal device moveable relative to the substrate table under thecontrol of a controller, the controller adapted to move the seal deviceduring at least some movements of the substrate table such that arelative velocity between the substrate table and the seal device issubstantially zero.

According to an aspect of the invention, there is provided alithographic projection apparatus, comprising: a projection systemconfigured to project a patterned beam of radiation onto a substrate; aliquid supply system configured to provide liquid in a space between theprojection system and a substrate, the space being smaller in plan thanthe substrate; and an enclosure configured to enclose a space radiallyoutwardly of the liquid supply system and above the substrate.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising pre-wetting a substrate prior toprojecting a patterned beam of radiation using a projection system ontothe substrate through a liquid, wherein liquid leaks from a spacebetween the projection system and the substrate to cover the substrate.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising projecting a patterned beam of radiationusing a projection system onto the substrate through a liquid, whereinliquid leaks from a space between the projection system and thesubstrate to cover the substrate and the liquid comprises an additivefor lowering the contact angle of the liquid on the substrate.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising projecting a patterned beam of radiationonto a substrate through a liquid wherein the liquid is supplied by aliquid supply system and any liquid escaping from the liquid supplysystem is removed by a liquid removal system which surrounds the liquidsupply system and moves relative to the liquid supply system.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising projecting a patterned beam of radiationusing a projection system through a liquid onto a substrate, wherein asealing device surrounds the substrate and seals liquid on a surface ofthe substrate, a substrate table holding the substrate, or both, andwherein the sealing device is moved relative to the substrate table sothat, during at least some movements of the substrate table, therelative velocity between the substrate table and the sealing device isreduced over the relative velocity which would exist if the sealingdevice remained stationary relative to the projection system.

According to an aspect of the invention, there is provided a devicemanufacturing method comprising projecting a patterned beam of radiationthrough a liquid onto a substrate, wherein the liquid is provided usinga liquid supply system and a space radially outwardly of the liquidsupply system is enclosed and maintained at a high vapor pressure ofliquid.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts, in cross-section, a barrier member acting as a liquidsupply system which may be used in an embodiment of the presentinvention as a liquid supply system or a liquid removal system or asealing device;

FIG. 6 illustrates, in cross-section, another barrier member which isbeing used as a liquid supply system which may be used in an embodimentof the present invention as a liquid supply system or a liquid removalsystem or a sealing device;

FIG. 7 illustrates, in cross-section, a liquid supply system and aliquid removal system in accordance with an embodiment of the presentinvention;

FIG. 8 depicts, in cross-section, an embodiment of the presentinvention;

FIG. 9 illustrates, in plan, a variant of the embodiment in FIG. 8;

FIG. 10 illustrates, in cross-section, the embodiment of FIG. 9;

FIG. 11 illustrates, in perspective view, a detail of an embodimentillustrated in FIG. 12;

FIG. 12 illustrates, in perspective view, a further apparatus embodimentof the present invention;

FIG. 13 illustrates, in perspective view, a close-up of a plate of theembodiment of FIG. 12; and

FIG. 14 illustrates, in plan, a substrate swap in the apparatus of FIGS.11-13.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL configured to condition        a radiation beam B (e.g. UV radiation or DUV radiation);    -   a support structure (e.g. a mask table) MT constructed to        support a patterning device (e.g. a mask) MA and connected to a        first positioner PM configured to accurately position the        patterning device in accordance with certain parameters;    -   a substrate table (e.g. a wafer table) WT constructed to hold a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioner PW configured to accurately position the        substrate in accordance with certain parameters; and    -   a projection system (e.g. a refractive projection lens system)        PS configured to project a pattern imparted to the radiation        beam B by patterning device MA onto a target portion C (e.g.        comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure holds the patterning device in a manner thatdepends on the orientation of the patterning device, the design of thelithographic apparatus, and other conditions, such as for examplewhether or not the patterning device is held in a vacuum environment.The support structure can use mechanical, vacuum, electrostatic or otherclamping techniques to hold the patterning device. The support structuremay be a frame or a table, for example, which may be fixed or movable asrequired. The support structure may ensure that the patterning device isat a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables (and/or two or more support structures). In such“multiple stage” machines the additional tables may be used in parallel,or preparatory steps may be carried out on one or more tables while oneor more other tables are being used for exposure.

Referring to FIG. 1, the illuminator IL receives a radiation beam from aradiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AD for adjusting the angularintensity distribution of the radiation beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the illuminator IL maycomprise various other components, such as an integrator IN and acondenser CO. The illuminator may be used to condition the radiationbeam, to have a desired uniformity and intensity distribution in itscross-section.

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS,which focuses the beam onto a target portion C of the substrate W. Withthe aid of the second positioner PW and position sensor IF (e.g. aninterferometric device, linear encoder or capacitive sensor), thesubstrate table WT can be moved accurately, e.g. so as to positiondifferent target portions C in the path of the radiation beam B.Similarly, the first positioner PM and another position sensor (which isnot explicitly depicted in FIG. 1) can be used to accurately positionthe patterning device MA with respect to the path of the radiation beamB, e.g. after mechanical retrieval from a mask library, or during ascan. In general, movement of the support structure MT may be ‘realizedwith the aid of a long-stroke module (coarse positioning) and ashort-stroke module (fine positioning), which form part of the firstpositioner PM. Similarly, movement of the substrate table WT may berealized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the supportstructure MT may be determined by the (de-)magnification and imagereversal characteristics of the projection system PS. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

The solutions for providing liquid between a final element of theprojection system PS and the substrate can be classed into two generalcategories. These are the bath type solutions in which the whole of thesubstrate. W is immersed in a bath of liquid and the so called localizedliquid supply systems in which liquid is only provided to a localisedarea of the substrate. In the latter category, the space filled byliquid is smaller in plan than the top surface of the substrate and thearea filled with liquid remains stationary relative to the projectionsystem PS whilst the substrate W moves underneath that area. Fourdifferent types of localized liquid supply systems are illustrated inFIGS. 2-6. The liquid supply systems disclosed in FIGS. 2-4 weredescribed above.

FIG. 5 schematically depicts a localized liquid supply system with abarrier member, which extends along at least a part of a boundary of thespace between the final element of the projection system and thesubstrate table. The barrier member is substantially stationary relativeto the projection system in the XY plane though there may be somerelative movement in the Z direction (in the direction of the opticalaxis). In an embodiment, a seal is formed between the barrier member andthe surface of the substrate and may be a contactless seal such as a gasseal.

The barrier member 12 at least partly contains liquid in the space 11between a final element of the projection system PL and the substrate W.A contactless seal 16 to the substrate may be formed around the imagefield of the projection system so that liquid is confined within thespace between the substrate surface and the final element of theprojection system. The space is at least partly formed by the barriermember 12 positioned below and surrounding the final element of theprojection system PL. Liquid is brought into the space below theprojection system and within the barrier member 12 by liquid inlet 13and may be removed by liquid outlet 13. The barrier member 12 may extenda little above the final element of the projection system and the liquidlevel rises above the final element so that a buffer of liquid isprovided. The barrier member 12 has an inner periphery that at the upperend, in an embodiment, closely conforms to the shape of the projectionsystem or the final element thereof and may, e.g., be round. At thebottom, the inner periphery closely conforms to the shape of the imagefield, e.g., rectangular though this need not be the case.

The liquid is contained in the space 11 by a gas seal 16 which, duringuse, is formed between the bottom of the barrier member 12 and thesurface of the substrate W. The gas seal is formed by gas, e.g. air orsynthetic air but, in an embodiment, N₂ or another inert gas, providedunder pressure via inlet 15 to the gap between barrier member 12 andsubstrate and extracted via outlet 14. The overpressure on the gas inlet15, vacuum level on the outlet 14 and geometry of the gap are arrangedso that there is a high-velocity gas flow 16 inwards that confines theliquid. The force of the gas on the liquid between the barrier member 12and the substrate W contains the liquid in a space 11. Thoseinlets/outlets may be annular grooves which surround the space 11 andthe flow of gas 16 is effective to contain the liquid in the space 11.Such a system is disclosed in United States patent applicationpublication no. US 2004-0207824, hereby incorporated in its entirety byreference.

Other solutions are possible and, as will be described below, anembodiment of the present invention may use any type of localized liquidsupply system as the liquid supply system and indeed, as describedbelow, the means for forming the seal between the barrier member 12 andthe substrate W can be used in the liquid removal system or sealingdevice of an embodiment of the present invention.

One or more localized liquid supply systems seal between a part of theliquid supply system and a substrate W. Relative movement of that partof the liquid supply system and the substrate W may lead to breakdown ofthe seal and thereby leaking of liquid.

FIG. 6 illustrates a barrier member 12 which is part of a liquid supplysystem. The barrier member 12 extends around the periphery of the finalelement of the projection system PS such that the barrier member (whichis sometimes called a seal member) is, for example, substantiallyannular in overall shape. The projection system PS may not be circularand the outer edge of the barrier member 12 may also not be circular sothat it is not necessary for the barrier member to be ring shaped and itcould also be other shapes so long as it has a central opening throughwhich the projection beam may pass out of the final element of theprojection system PS through liquid contained in the central opening andonto the substrate W. The barrier member 12 may be, for example,substantially rectangular and is not necessarily the same shape as thefinal element of the projection system PS is at the height of thebarrier member 12.

The function of the barrier member 12 is to at least partly maintain orconfine liquid in the space between the projection system PS and thesubstrate W so that the projection beam may pass through the liquid. Thetop level of liquid is simply contained by the presence of the barriermember 12 and the level of liquid in the space is maintained such thatthe liquid does not overflow over the top of the barrier member 12. Aseal is provided between the bottom of the barrier member 12 and thesubstrate W. In FIG. 6 a seal device is configured to provide acontactless seal and is made up of several components. Working radiallyoutwardly from the optical axis of the projection system PS, there isprovided a (optional) flow plate 50 which extends into the space (thoughnot into the path of the projection beam) which helps maintainsubstantially parallel flow of the immersion liquid out of outlet 20across the space. The flow control plate has through holes 55 in it toreduce the resistance to movement in the direction of the optical axisof the barrier member 12 relative to the projection system PS and/orsubstrate W.

Moving radially outwardly along the bottom of the barrier member 12there is then provided an outlet 60 which provides a flow of liquid in adirection substantially parallel to the optical axis towards thesubstrate. This flow of liquid is used to help fill any gaps between theedge of the substrate W and the substrate table WT which supports thesubstrate. If this gap is not filled with liquid, bubbles may beincluded in the liquid in the space between the projection system PS andthe substrate W when an edge of the substrate W is passed under theseal. This is undesirable as it may lead to deterioration of the imagequality.

Radially outwardly of the outlet 60 is a extractor assembly 70 toextract liquid from between the barrier member 12 and the substrate W.The extractor 70 will be described in more detail below and forms partof the contactless seal which is created between the barrier member 12and the substrate W.

Radially outwardly of the extractor assembly 70 is a recess 80 which isconnected through an inlet 82 to the atmosphere and via an outlet 84 toa low pressure source. Radially outwardly of the recess 80 is a gasknife 90. An arrangement of the extractor, recess and gas knife isdisclosed in detail in U.S. patent application No. 60/643,626, filed 14Jan. 2005. However, in that document the arrangement of the extractorassembly is different.

The extractor assembly 70 comprises a liquid removal device or extractoror inlet 100 such as the one disclosed in United States patentapplication publication no. US 2006-0038968, incorporated herein itsentirety by reference. Any type of liquid extractor may be used. In anembodiment, the liquid removal device 100 comprises an inlet which iscovered in a porous material 110 which is used to separate liquid fromgas to enable single-liquid phase liquid extraction. A chamber 120downstream of the porous material 110 is maintained at a slight underpressure and is filled with liquid. The under pressure in the chamber120 is such that the meniscuses formed in the holes of the porousmaterial prevent ambient gas from being drawn into the chamber 120 ofthe liquid removal device 100. However, when the porous surface 110comes into contact with liquid there is no meniscus to restrict flow andthe liquid can flow freely into the chamber 120 of the liquid removaldevice 100. The porous surface 110 extends radially inwardly along thebarrier member 12 (as well as around the space) and its rate ofextraction varies according to how much of the porous material 110 iscovered by liquid.

During scanning of the substrate W (during which the substrate movesunder the barrier member 12 and projection system PS) the meniscus canbe drawn either towards or away from the optical axis by a drag forceapplied by the moving substrate. This can lead to liquid loss which mayresult in evaporation of the liquid and thereby cooling of the substrateand consequent shrinkage and overlay errors as described above. Liquidstains may also or alternatively be left behind from interaction betweenthe liquid droplets and resist photochemistry. A plate 200 is providedbetween the liquid removal device 100 and the substrate W so that thefunction of liquid extraction and the function of meniscus control canbe separated from one another and the barrier member 12 may be optimizedfor each.

The plate 200 is a divider or any other element which has the functionof splitting the space between the liquid removal device 100 and thesubstrate W into two channels, an upper channel 220 and a lower channel230 wherein the upper channel 220 is between the upper surface of theplate 200 and the liquid removal device 100 and the lower channel 230 isbetween the lower surface of the plate 200 and the substrate W. Eachchannel is open, at its radially innermost end, to the space. Thethickness of the plate is not critical. Although as illustrated in FIG.6 the upper channel 220 extends horizontally, this is not necessarilythe case. The reason for the upper channel 220 extending horizontally inFIG. 6 is because of the structural arrangement of the components.However, the upper channel 220 could also extend vertically or any wherebetween horizontally and vertically. The gravitational pressure on theliquid in the upper channel 220 is very low and, if necessary, can becounteracted by applying an under pressure, for example through liquidremoval device 100 itself or through another passage such as breathingholes 250 described below.

In an embodiment, the upper channel 220 between the liquid removaldevice 100 and the plate 200 is narrower than the lower channel 230between the plate 200 and the substrate W. The lower channel is between250 mm and 50 μm high, or between 100 and 60 μm depending on design(viscous drag length from flow pattern), fluid parameters (viscosity,density, surface tension) and surface properties (contact angleresulting from binding energy surface/liquid and liquid surfacetension). The upper channel 220 has a stronger capillary action, forinstance by making it 2 to 3 times narrower than the lower channel.Alternatively or additionally, the upper channel 220 may be made with asurface which is more liquidphillic than the lower channel 230. However,the upper channel 220 may also be wider than the lower channel 230. Ifthe upper channel 220 is too narrow, liquid does not flow in thatchannel because the frictional resistance is too large and the pinnedmeniscus is fully loaded with hydrodynamic forces. Thus, if the upperchannel 220 is made wider, for example in the region of 150 μm, than thelower channel 230 which could be perhaps 60 μm, these difficulties maybe overcome. Above a channel width of 250 μm the capillary action isreduced. In order to promote capillary action, the upper channel 220could be made liquidphillic or a height step close to the meniscusbetween the plate 200 and the liquid removal device 100 may be made suchthat the channel radially inwardly is wider than radially outwardly.

An under pressure may be applied in the upper channel 220, rather thanleaving it open to the atmosphere through breathing holes 250 e.g.through the holes 250. In this way the upper channel 220 may be madewider.

With the plate 200, there are two meniscuses 310, 320. A first meniscus310 is positioned above the plate 200 and extends between the poroussurface 110 and the top surface of the plate 200 and a second meniscus320 which is positioned underneath the plate 200 and which extendsbetween the plate and the substrate W. In this way the extractorassembly 70 may be optimized for control of the first meniscus 310 foroptimum extraction of liquid and for positional control of the secondmeniscus 320 such that the viscous drag length for the second meniscus320 is reduced and the characteristics, in particular of the plate 200,are optimized to make it energetically favorable for the second meniscus320 to remain adhered to the plate 200 such that the scan speed of thesubstrate W beneath the barrier member 10 may be increased. Capillaryforces acting on the second meniscus 320 are outwards and are balancedby an under pressure in the liquid adjacent the second meniscus 320 sothat the second meniscus 320 stays substantially still. Higher loadingon the second meniscus 320, for example by viscous drag and inertia,results in a lowering of the contact angle of the second meniscus 320with the surface.

One or more breathing holes 250 are provided at the radially outwardmost end of the plate 200 such that the first meniscus 310 is free tomove inwardly and outwardly beneath the porous material 110 so that theextraction rate of the liquid removal device 100 may vary according tohow much of the porous material 110 is covered by liquid. As illustratedin FIG. 6 the second meniscus 320 adheres to a lower inward edge of theplate 200.

In FIG. 6 the inner most bottom edge of the plate 200 is provided with asharp edge so as to pin the second meniscus 320 substantially in place.The radius of the edge is, in an embodiment, less than 0.1 mm, less than50 μm, less than 20 μm or about 10 μm.

An alternative or additional way of pinning the second meniscus 320 isto change the surface properties of the surface of the plate 200 towhich the second meniscus 320 adheres. For example, a change from aliquidphilic to a liquidphobic surface in a radially outward directionon the plate 200 could also result in pinning of the second meniscus 320at that change because the shape of the meniscus will need to invert forit to pass from the liquidphilic to the liquidphobic surface.Additionally or alternatively, the second meniscus 320 may be pinned bychanging the surface of the plate 200 from a rough to a smooth surface.When fully wetted the rough surface can act as a meniscus trap. If thesurface is not fully wetted and the liquid is only on the peaks of theroughness, a rough surface can act liquidphobic such as in the so calledlotus effect. Also or additionally, electro wetting could be used tolocally trap the meniscus. This has an advantage in that it can beturned on and off.

Although not specifically illustrated in FIG. 6, the liquid supplysystem has an arrangement to deal with variations in the level of theliquid. This is so that liquid which builds up between the projectionsystem PS and the barrier member 12 can be dealt with and does notspill. Such a build-up of liquid might occur during relative movement ofthe barrier member 12 to a projection system PS described below. One wayof dealing with this liquid is to provide the barrier member 12 so thatit is very large so that there is hardly any pressure gradient over theperiphery of the barrier member 12 during movement of the barrier member12 relative to the projection system PS. In an alternative or additionalarrangement, liquid may be removed from the top of the barrier member 12using, for example, an extractor such as a single phase extractorsimilar to the extractor 120.

One of the difficulties with any of the localized area liquid supplysystems is that it is difficult to contain all of the immersion liquidand to avoid leaving some behind on the substrate as the substrate movesunder the projection system. In order to avoid liquid loss, the speed atwhich the substrate moves under the liquid supply system must belimited. This is particularly so with immersion liquids capable ofgenerating high values of NA in the immersion lithography apparatusbecause they tend to have a lower surface tension than water as well asa higher viscosity. Breakdown speed of a meniscus scales with surfacetension over viscosity so that high NA liquids may be far harder tocontain. Leaving liquid behind on the substrate in only certain areasmay lead to temperature variations throughout the substrate due toevaporation of the immersion liquid left behind on only certain areas ofthe substrate and thus leading to overlay errors. Also or alternatively,as the immersion liquid evaporates, it is possible that drying stainscan be left behind on the substrate W. Also or alternatively, the liquidmay diffuse into the resist on the substrate leading to inconsistenciesin the photochemistry of the top surface of the substrate. Although abath type solution (i.e. where the substrate is submerged in a containerof liquid) would alleviate many of these problems, substrate swap in theimmersion apparatus is particularly difficult with a bath type solution.An embodiment of the present invention addresses one or more of theseissues as will be described below.

In an embodiment of the present invention a localized liquid supplysystem LSS is used to provide liquid below the projection system PSabove the substrate W. A flow of liquid in that area is generated. Forthis purpose any localized liquid supply system may be used, e.g. anyone of the types shown in FIGS. 2-6, such as those illustrated in FIG. 5or 6 or variants thereof. However, the seal formed between the localizedliquid supply system LSS and the substrate W does not need to be made tobe particularly well and may in fact be entirely missing. For example,all of the components on the bottom side of the barrier member 12 may bemissing from the FIG. 6 embodiment and optionally replaced only with afluid seal (gas or liquid) such as that illustrated in FIG. 5. However,the type of seal or indeed complete absence of a seal is not critical toan embodiment of the present invention. The design is chosen such that afilm of liquid covers the whole of the top surface of the substrate W asis illustrated in FIGS. 7 a and b. This film of liquid is then containedby a sealing device such as a liquid removal system LRS which may againbe comprised of a barrier member 12 similar to that illustrated in FIG.5 or 6. The liquid removal system LRS is primarily designed with sealingand liquid removal in mind. The liquid removal may occur through a sealformed between the barrier member and the substrate W or may beperformed by a separate functional element.

In an embodiment, a contactless seal (for example a fluid seal in theform of a gas or liquid seal) is formed between the liquid removalsystem LRS and the substrate W or substrate table WT. A controller 50 isprovided to reduce the relative velocity of the liquid removal systemLRS relative to the substrate W from that which it would be if theliquid removal system LRS were to be held stationary relative to theprojection system PS during step and scanning motions of the substratetable WT. The reduction in this relative velocity increases the sealingperformance of the contactless seal. In an embodiment, the liquidremoval system LRS is moved to mirror the movement of the substratetable WT such that the relative velocity between the liquid removalsystem LRS and the substrate table WT during step and scan motions issubstantially zero. However, this is not necessarily the case and therecan be some relative velocity between those two items so long as therelative velocity is reduced below the level present if no movement ofthe liquid removal system LRS occurred and it were fixed relative to theprojection system PS. The reduction in this relative velocity means thata better contactless seal can be formed between the substrate table WTor the substrate W and the liquid removal system LRS.

The liquid supply system LSS is held substantially stationary relativeto the projection system PS during imaging such that, as can be seenfrom a comparison of FIGS. 7 a and b, during imaging the liquid removalsystem LRS is substantially stationary relative to the substrate W whichmoves relative to the projection system PS whereas the liquid supplysystem LSS stays stationary relative to the projection system PS but thesubstrate W moves relative to the liquid supply system LSS. However,because there is no requirement for a particularly good seal between theliquid supply system LSS and the substrate W it is possible to move thesubstrate W at a higher velocity under the projection system PS thanpreviously because leaking from the liquid supply system LSS does notmatter. Indeed, it may be useful to manufacture the liquid supply systemLSS from (or coat it in) a material with which the immersion liquid hasa low contact angle e.g. less than 50°, less than 30° or less than 20°.The same applies for the substrate W and the substrate table WT.Furthermore, an advantage of this present system over a bath typesolution is that force is not generally transferred from the movingsubstrate table WT into the projection system PS through the liquid 11because the liquid supply system LSS generally acts as a barriershielding or isolating the projection system PS from the liquid 11 onthe substrate W. In an embodiment, the liquid supply system LSS isattached to the reference frame RF to which the projection system PS isalso attached. The substrate table WT is attached to the base frame BF(from which the reference frame RF is dynamically isolated) and theliquid removal system LRS can be attached to the base frame BF viaactuators which drive it.

The liquid removal system LRS of FIG. 7 is illustrated as being largeenough to surround the whole of the substrate W. This is advantageousbecause it allows the whole top surface of the substrate W to be coveredin liquid thereby both maintaining the temperature of the substrate Wsubstantially constant across its whole surface as well as maintainingthe amount of dissolution of the top coat of the substrate into theimmersion liquid (and diffusion of the immersion liquid into the topcoat) across the whole top surface of the substrate W substantiallyconstant. The liquid removal system LRS may also be large enough tocover any sensors on the top surface of the substrate table WT, forexample, which are imaged by the projection beam from the projectionsystem PS through immersion liquid. If this is not the case, the liquidremoval system LRS may be moved to allow imaging of the sensors.

As will be appreciated from the above, a function of the liquid removalsystem LRS is to form a seal between it and the substrate table WT orsubstrate W. The liquid could actually be removed by a differentcomponent but it is convenient to provide the function of liquid removaland sealing in the same unit as in the described embodiments.

A similar principle is disclosed in PCT patent application publicationno. WO 2005/064405. In that document a barrier member is also used toprovide liquid to a space between a final element of the projectionsystem PS and a substrate W but liquid is allowed to flow out of thatarea onto the whole top surface of the substrate. In WO 2005/064405 arim is provided around the outer edge of the top surface of thesubstrate table to prevent the liquid from contaminating other areas ofthe apparatus. Other solutions are also possible including allowing theliquid to drain off the top surface of the substrate table WT and to becollected under the substrate table WT. This may include an arrangementwhereby a component of the substrate table WT such as a chuck which isactuated by a short stroke actuator does not contain the liquid butwherein the liquid is allowed to flow off that chuck onto anothercomponent of the substrate table WT which other component is part of oris actuated by a long stroke positioning means. In another embodiment,similar to the embodiment disclosed in WO 2005/064405, liquid iscollected in drains in top surface of a substrate table WT positionedaround the outside of the substrate W or elsewhere on the substratetable WT.

As is illustrated in FIG. 7, a cover 500 may be provided between theliquid supply system LSS and the liquid removal system LRS to form anenclosure between the wall of the cover 500, the liquid supply systemLSS and the liquid removal system LRS, the top surface of the substrateW and part of the top surface of the substrate table WT. The enclosureis partly filled with the immersion liquid lying on the top surface ofthe substrate table W and substrate table WT and the remainder of theenclosure is filled with gas. A humidity controller may be used tocontrol the partial pressure of the immersion liquid in the gas. Forexample, if the partial pressure (humidity) of immersion liquid in thatgas is maintained at 100%, or close to 100% such as at 80% or 90%,evaporation of the immersion liquid from the top of the substrate willbe reduced or prevented thereby to help minimize temperature changesand/or drying stains. A bearing is provided between the cover 500 andthe liquid removal system LRS and this embodiment of a single cover 500which is substantially stationary relative to the projection system PSmay take up a significant amount of space in a lithographic projectionapparatus. However, other arrangements are possible which do not take upso much space and two such examples are illustrated in FIGS. 8-10.

With a contactless seal being formed between the liquid removal systemLRS and the substrate table WT, substrate swap after finishing exposureof one substrate prior to exposing a further substrate becomes possible.This may be achieved without removing all of the liquid from the liquidsupply system LSS and even without removing all of the liquid fromwithin the liquid removal system LRS. During substrate swap a dummysubstrate may be moved under the liquid removal system LRS and liquidsupply system LSS as the substrate table WT holding the exposedsubstrate W is moved out from under the liquid removal system LRS andliquid supply system LSS. Thus, the final element of the projectionsystem PS can be maintained wet during substrate swap. Then the dummysubstrate is moved out from under the liquid removal system LRS andliquid supply system LSS as the new substrate W is moved under thosecomponents. Alternatively it is possible to only maintain the liquidsupply system LSS running during substrate swap as this is really theonly component which should be maintained running so that the finalelement of the projection system PS is maintained wet during substrateswap. Direct swap, without the intervening dummy substrate is alsopossible.

In the embodiment of FIG. 8 the solid cover 500 is replaced by a bellowtype cover 510. The two dimensional bellows allow limited relativemovement of the liquid removal system LRS to the liquid supply systemLSS.

FIGS. 9 a and b show a further alternative to the cover 500 of FIG. 7.In this embodiment the cover comprises two plates (e.g., discs). Afirst, larger plate 800 is rotatable relative to the liquid removalsystem LRS. A second plate 810 is positioned in or above a through holein the first plate 800 and is rotatable about the central axis of thethrough hole. A through hole 830 in the second plate is filled with theliquid supply system LSS (not illustrated in FIGS. 9 a and b). Byrotation of the first and second plates 800, 810 and translation of thecentral axis of those plates with respect to the projection system PSthe through hole 830 can be placed above any point of the substrate Wwhile the first plate 800 still covers all of the substrate W therebyforming the enclosure.

FIG. 10 illustrates, in cross-section the first plate 800, second plate810 and the through hole 830 in which the liquid supply system LSS ispositioned.

Although the embodiment of FIGS. 9 and 10 have been illustrated with thesmaller plate 810 being positioned in the through hole in the largeplate 800, this may not necessarily be so and other constructionalarrangements could be used. For instance, the plate 810 may be supportedby and rest on a bearing on the upper surface of the first plate 800.Furthermore, translational movements of the plates 800, 810 to oneanother and to the substrate W and even to the liquid removal system LRSmay be possible. Although the use of only two plates are described, thesame principle can be applied with any number of plates fitting in or onthrough holes in the larger plates. For example, a third plate could beplaced in the through hole 830 of the second plate 810 and rotated inthat hole. The liquid supply system LSS would then fit in a through holein the third plate. Up to five plates or more is practical.

FIGS. 11 to 14 illustrate a further embodiment of the present invention.In this embodiment, like all of the other embodiments, liquid isprovided to a space between the final element of the projection systemand the substrate W and is allowed to leak from that space to cover thewhole of the substrate. This embodiment is particularly suitable for usewith a substrate table WT whose position is measured using encoder heads980 attached to the substrate table WT. Encoder plates 990 arepositioned above the substrate table WT and they interact with theencoder heads 980 to provide positional information regarding thesubstrate table WT. In such an arrangement it is necessary for anunobstructed path to be present between at least three of the encoderheads 980 and their respective encoder plates 990 positioned above them.The embodiment of FIGS. 11-14 allows for this as well as for forming anenclosure above the surface of the substrate W covered in liquid for usein reducing evaporation from the liquid from a surface of the substrate.

In this embodiment a skirt 1000 is provided on the substrate table WT.This skirt 1000 is fixed in the XY axis relative to the substrate tableWT but is actuatable in the Z axis (i.e. it can be retracted into thetop surface of the substrate table WT or can be extended out of it).Thus the skirt 1000 which, during imaging, is stationary relative to thesubstrate table WT takes the place of the liquid removal system LRS ofthe embodiment of FIG. 7. The seal between the skirt 1000 and substratetable WT may be made as a seal with physical contact such that a liquidtight seal is formed. The skirt 1000 provides a barrier to both liquidand vapor, i.e. to fluids. The enclosure is then formed with plates1100, 1210, 1220, 1230 which will be described below in relation to FIG.12.

The substrate table WT is divided in two parts. The substrate tableillustrated in FIGS. 11 and 12 is only the top part of the substratetable WT which is often referred to as the chuck. The other part of thesubstrate table WT is moved with a long stroke actuator and the chuck ismoved relative to the other part by a short stroke actuator. The shortstroke actuator moves the chuck relative to the second part of thesubstrate table WT and the long stroke actuator moves the substratetable WT as a whole relative to the base frame. In order to avoidoverlay errors the skirt 1000 is attached to the second part of thesubstrate table WT and the skirt 1000 is not in contact with the chuckat all so that it does not affect the overlap accuracy of the apparatus.One or more lever springs mounted to the long stroke module act asguides to ensure that the skirt has the correct shape.

As can be seen in FIG. 12, a central fixed plate 1100 is included in theapparatus. This fixed plate also incorporates a liquid supply system LSSconfigured to provide liquid between the final element of the projectionsystem PS and the substrate W as in the above described embodiments. Theplate 1100 has a through hole 1105 in it to accommodate the finalelement of the projection system PS. The liquid supply system LSSprovides a liquid flow across that through hole 1105 in much the sameway as the liquid supply system LSS provides a flow of liquid in theembodiment of FIG. 7.

The plate 1100 and integral liquid supply system LSS are held stationaryrelative to the projection system PS in the X-Y direction and the plate1100 extends or is elongate in the Y-direction. The substrate table WTis moved under the projection system PS and plate 1100 during scanning.

In the embodiment illustrated, the substrate table WT is provided withfour encoder heads 980 at or near each corner of the substrate table WT.In order to accurately to determine the position of the substrate tableWT at least three of the four encoder heads 980 should have anunobstructed view of encoder plates 990 which are positioned above thesubstrate table WT and which are fixed in position relative to theprojection system PS. In FIG. 12, the encoder plates 990 have been drawnnext to the remainder of the apparatus for clarity. In fact the encoderplates are positioned above the substrate table WT such that each of thefour encoder plates is positioned above the respective encoder head 980such that it is above the encoder head 980 during the whole movement ofthe substrate table WT under the projection system PS.

Four independently moveable plates 1210, 1220, 1230 and 1240 areprovided to form the top wall of the enclosure. The plates can be seenas being used to minimize the flow of gas into and out of the minienvironment created above the substrate W. The plates 1210, 1220, 1230and 1240 are actuatable along the Y axis using actuators 1300 (which maybe connected to the base frame or BF or to the metrology frame MF whichsupports the projection system). A gap is maintained between the variousplates and between the skirt 1000 and the plates so that there is nophysical contact. Further the gap is kept small enough to ensure thatthe humidity in the enclosure formed by the skirt and plates above thesubstrate W can be maintained at a higher relative humidity of immersionliquid than the atmosphere outside of the enclosure. Thus the need forcomplicated seals may be avoided.

When the substrate table WT moves under the projection system PS and thefixed plate 1100, the area above the substrate W which needs to becovered by the plates 1210, 1220, 1230, 1240 will change. Furthermore,at least three of the four encoder heads 980 should not be covered bythe plates at any one time and thus a reason for the use of four platesin this embodiment. The plates are shaped such that it is possible tocover the required area with two moveable plates 1210, 1220 and 1230,1240 on either side of the fixed plate 1100. Each of the plates isshaped as a parallelogram and is independently moveable of the otherplate on the same side of the fixed plate 1100.

As can be seen in FIG. 12, when the substrate table WT is positionedsuch that more of its area is on the same side of the center plate 1100as a pair of plates 1210,1220, the bases of those plates 1210,1220 arebrought closer together so that their free ends closest to the fixedplate 1110 are spread apart. Because of the specific shape of the plates1210, 1220 the encoder heads 980 on that side are not covered by theplates but the whole of the area inside of the skirt 1000 is covered bythe plates. On the other side of the fixed plate 1110, as can be seen,the bases of the plates 1230, 1240 attached to the actuator 1300 arefurther apart than on the other side. As a result their free ends arecloser together so as to avoid covering the encoder heads 980 but stillcovering the area inside the skirt 1000.

If it were not for the encoder heads 980 requiring a free path to theencoder plates 990 and the position of the substrate table WT were to bemeasured using interferometers attached to the metrology frame andencoding plates attached to the edge of the substrate table WT, it wouldbe possible to provide a single rectangular-shaped plate on either sideof the fixed plate 1100 which would be translated parallel to the lengthof the fixed plate. In this case the plates would need to be wide enoughto cover the entire stroke of the chuck. This would still be possiblewith encoder heads 980 and encoder plates 990 as shown in FIGS. 11 and12 if the encoder heads are placed far enough out from the skirt 1000.However this leads to an increase in the size of the apparatus.

During scanning, when the substrate table WT moves in the Y-direction,the plates 1210, 1220, 1230, 1240 move with it in the Y-direction. Ifthe substrate table WT moves in the X-direction the relative positionsof the plates on either side of the fixed plate 1100 are changed. Thusif the substrate table WT in FIG. 12 were to be moved further to theleft in the X-direction, the plates on the right hand side of the fixedplate 110 would be moved further away from one another whereas theplates on the left hand side of the fixed plate 1100 would be movedcloser to each other. In this way the integrity of the enclosure wouldbe maintained while the encoder heads 980 would not be covered.

As will be appreciated, the lower plate in each pair of plates (1220 and1240) always has an edge in the same position relative to the sensor. Asthe substrate table WT moves in the X-direction, the portion of thatedge that is adjacent to the sensor changes. Accordingly, the skirt 1000is provided with a step 1010 to take account of the different height ofthe plates. However, the position of the step does not need to change asthe substrate table WT moves around.

As will be appreciated, the fixed plate 1100 should be long enough tocover the joint between the pairs of cover plates over the full lengthof the stroke of the chuck.

The arrangement illustrated in FIGS. 11 and 12 is advantageous becausethe encoder heads 980 are close together in the Y-direction. However,the sensors are placed further out in the X-direction than they wouldneed to be without the plates. Accordingly, it would be possible to usethe same arrangement of plates in the X-direction as in the Y-directionleading to two levels of plates. This is at the expense of complexity.

The gap between each of the plates and the plates and the skirt and theplates and the fixed plate is of the order of 0.2 to 0.5 mm but may beas small as 0.1 mm or smaller. With this size gap, it is possible to getup to 98% relative humidity in the enclosure.

The reason that the skirt 1000 is actuated in the Z-direction is so thatthe substrate table WT can be moved in and out from under the projectionsystem PS, the liquid supply system LSS and any metrology unit. Thosecomponents often need to approach the substrate WT very closely. Thus ifthe substrate table WT is to be moved with the skirt protruding from it,it would be necessary to actuate (lower) the whole of the substratetable WT in the Z-direction in order to avoid those components collidingwith the skirt 1000 which may be between 3 and 12 mm above the surfaceof the substrate (in an embodiment, between 5 and 6 mm). Therefore, inorder to avoid collision, the skirt 1000 is raised before the exposuresequence and lowered thereafter. The skirt may be made of carbon fiberor some fowl of brushes or an elastic material.

In an embodiment, the plates 1210, 1220, 1230, 1240 are manufacturedfrom a lightweight components such as a sandwich structure or ahoneycomb structure perhaps of carbon fiber or aluminum.

FIG. 13 shows a plate 1210, 1220, 1230, 1240 in detail. As will be seen,the plate is manufactured with a plurality of holes 1215 in it which arecovered with an elastic membrane. This membrane is elasticallydeflectable. This means that movement of the plate 1210 in gas will beless damped than would result if it were not for the holes 1215 coveredwith the membrane. This is a particular difficulty because the distancebetween the encoder plates 990 and the plates 1210, 1220, 1230, 1240 mayonly be a few mm or even as little as 0.5 mm. Because the encoder platesare mounted relative to the metrology frame whereas the moveable plates1210, 1220, 1230, 1240 are mounted relative to the base frame, and themetrology frame is mounted on flexible mounts relative to the baseframe, the plates 1210, 1220, 1230, 1240 can move relative to theencoder plates 990 in the Z-direction and this could cause gas dampingwhich may result in cross talk between the moveable plates and encoderplates. Thus providing the plates 1210, 1220, 1230, 1240 with throughholes 1215 covered in a flexible membrane prevents gas from flowingthrough butterfly plates but the membrane can expand upwards anddownwards to accommodate the gas flow caused by relative movements ofthose plates to the encoder plates 990.

FIG. 14 shows the procedure in which the plates 1210, 1220, 1230, 1240are transferred from one substrate table WT to another in a dualsubstrate apparatus configuration. Basically the plates on one side ofthe fixed plate 1100 are moved in unison together from covering thefirst substrate table to the second substrate table. During thisprocedure only one encoder head 980 will be covered at any one time (seestep 2). Once the plates on one side of the fixed plate 1100 have beenmoved into position over the second substrate table, the plates on theother side of the fixed plate 1100 are moved from the first table to thesecond table. During this whole procedure both of the substrate tablesWT remain stationary. Once all four plates have been moved to the newsubstrate table, both substrate tables WT can be moved so that the newsubstrate table is positioned under the projection system PS.

In an embodiment, the encoder plates themselves are used in place of themoveable plates. The encoder plates are fixed relative to the projectionsystem PS in any case and are of a large enough size to be able to coverthe enclosure throughout all of the stroke of the substrate table WT.Condensation of the immersion liquid on the plates may be a difficultyand steps may need to be taken to avoid that.

All of the above embodiments have the whole surface of the substratecovered in a liquid i.e. full wetting behavior so that no droplets areformed but instead a continuous film. This may require pre-wetting ofthe surface of the substrate W to ensure that it is all wetted. The filmof liquid on the surface of the substrate not under the projectionsystem PS should be as thin as possible without the film layer breakingup. One way of making this easier is to add a surfactant or wettingagent to the immersion liquid. Alternatively or additionally, ahydrophilic layer may be provided on a substrate so that no additive maybe required. In general, the additive added to the immersion liquidshould be selected in order to provide a low contact angle of the liquidwith the surface of the substrate. The contact angle can be less than70°, less than 60°, less than 50°, less than 30° or less than 15°. Theadditive should be transparent to the radiation used in the projectionsystem to avoid heating due to adsorption or at least transparent enoughto ensure that enough radiation reaches the resist layer properly totransfer the image on the resist layer. Such heating could affect therefractive index of the fluid which is clearly undesirable. One additivewhich is suitable is Optiyield 93c which is produced by Air Products andChemicals, Inc.

In any of the above embodiments (particularly that of FIGS. 11-14) theimmersion liquid may be removed through an outlet which is stationaryrelative to the substrate table WT. If the outlet is actually throughthe substrate table WT, measures may be taken to reduce the chance ofinducing vibrations in the substrate table WT by the extraction or toallow evaporation in the extraction channel or allow a mixture of, gasand air into the extraction channel. This can be done by designing theextractor as a single phase extractor, for instance by using a porousmaterial in the same way as the single phase extractor as illustrated inFIG. 6 and as described above.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. For example, the invention may take the form of acomputer program containing one or more sequences of machine-readableinstructions describing a method as disclosed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above and whether the immersion liquid is provided in the formof a bath or only on a localized surface area of the substrate. A liquidsupply system as contemplated herein should be broadly construed. Incertain embodiments, it may be a mechanism or combination of structuresthat provides a liquid to a space between the projection system and thesubstrate and/or substrate table. It may comprise a combination of oneor more structures, one or more liquid inlets, one or more gas inlets,one or more gas outlets, and/or one or more liquid outlets that provideliquid to the space. In an embodiment, a surface of the space may be aportion of the substrate and/or substrate table, or a surface of thespace may completely cover a surface of the substrate and/or substratetable, or the space may envelop the substrate and/or substrate table.The liquid supply system may optionally further include one or moreelements to control the position, quantity, quality, shape, flow rate orany other features of the liquid.

The immersion liquid used in the apparatus may have differentcompositions, according to the desired properties and the wavelength ofexposure radiation used. For an exposure wavelength of 193 nm, ultrapure water or water-based compositions may be used and for this reasonthe immersion liquid is sometimes referred to as water and water-relatedterms such as hydrophilic, hydrophobic, humidity, etc. may be used.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1.-29. (canceled)
 30. A device manufacturing method comprisingprojecting a patterned beam of radiation using a projection system ontothe substrate through a liquid, wherein liquid leaks from a spacebetween the projection system and the substrate to cover the substrateand the liquid comprises an additive for lowering the contact angle ofthe liquid on the substrate.
 31. The method of claim 30, wherein theliquid, has a contact angle of less than 70° with the substrate.
 32. Adevice manufacturing method comprising projecting a patterned beam ofradiation onto a substrate through a liquid wherein the liquid issupplied by a liquid supply system and any liquid escaping from theliquid supply system is removed by a liquid removal system whichsurrounds the liquid supply system and moves relative to the liquidsupply system. 33.-34. (canceled)